1. Field of the Invention
The present invention relates to a method and apparatus for coating a solution on a surface of a hollow cylindrical substrate to form a coating layer and, more particularly, to a method and apparatus for forming a photosensitive layer on a surface of a drum used in an electrophotographic apparatus.
2. Description of the Related Art
In an electrophotographic apparatus such as a copying machine and a laser printer, an image is formed by using a photosensitive body consisting of a photo semiconductor. The surface of the photosensitive body is uniformly charged by corona discharge or the like. An electromagnetic wave representing an image of an original is projected on the charged surface of the photosensitive body to form an electrostatic latent image on this surface. A toner is attached to the latent image to visualize the latent image (development). The developed image is transferred to a transfer medium such as a sheet of paper. After image transfer, a residual toner left on the surface of the photosensitive body is scraped by a cleaning blade, and residual charge is neutralized upon radiation of light or corona discharge, thereby completing one copying cycle.
Inorganic photosensitive materials such as selenium, selenium-tellurium, arsenic selenide (As.sub.2 Se.sub.3), and zinc oxide (ZnO) have been used as photosensitive materials in the above electro-photographic apparatus. However, selenium and selenium-tellurium have low hardnesses and short service lives, are toxic to humans, and have low softening points. The charging capacity and photosensitivity of arsenic selenide are greatly degraded by optical fatigue In addition, arsenic selenide is toxic and has poor temperature characteristics. Zinc oxide has poor plate wear resistance.
Amorphous silicon or an organic photoconductive material has been recently used in place of the above inorganic photosensitive materials. Amorphous silicon has a high Vicker's hardness, high plate wear resistance, and high impact resistance. In addition, amorphous silicon has a high photosensitivity in a wide wavelength range from the entire visible light range to a near infrared range. However, amorphous silicon has a small charge capacity, tends to cause image tailing, and is expensive.
An organic photoconductive material is cheaper than amorphous silicon and does not cause pollution. In addition, the plate wear resistance and photosensitivity of the organic photoconductive material can be improved by proper selection of the material. In particular, an organic photosensitive material of a multi-layered structure consisting of a charge generating layer in which electrons and holes are generated and a charge transport layer in which the electrons and holes are transported has received a great deal of attention as a material having excellent properties.
In order to form a multi-layered photoconductive layer on a surface of a hollow cylindrical conductive substrate, the substrate is dipped in a solution of an organic photoconductive material in an organic solvent and is removed therefrom in the vertical direction. The substrate with an organic photoconductive layer is dried. In this dipping method, since the substrate is removed from the solution in the vertical direction, a thick portion as a sag is formed at the lower end portion of the substrate by a run of the solution. In addition, the solution flows to the inner surface of the lower end of the substrate. Therefore, the organic photoconductive material is applied to the lower end face and the inner surface of the lower end.
Conventional techniques for removing the thick portion at the lower end portion include a method of wiping the thick portion with a cleaning tape dampened with a solvent (Japanese Patent Disclosure (Kokai) No. 60-194459, and a method of applying a solvent to the thick portion with a rotating brush (Japanese Patent Disclosure (Kokai) No. 60-9731). A conventional method of removing a material from the lower end face and the inner surface of the lower end of the cylindrical substrate is exemplified by a method of spraying a solvent from a rotary nozzle to the inner wall surface of the lower end of the substrate (Japanese Patent Disclosure (Kokai) No. 60-168154).
According to the methods using the cleaning tape and the rotating brush, however, the material applied to the inner wall surface of the cylindrical substrate cannot be removed. In addition, wear of the brush produces dust to contaminate the working atmosphere. In addition, the brush must be frequently replaced. The method of spraying the solvent from the nozzle cannot remove the material from the thick portion of the lower end portion of the substrate and the lower end face of the substrate.
There is no conventional method and apparatus for removing the thick portion from the lower end portion of the substrate and a material from the inner wall surface of the lower end of the substrate and the lower end face.